The operating voltage of a permanent magnet generator is a function of the coercive force of the magnets. The coercive force tolerance of magnets is typically greater than the acceptable voltage tolerance for the generator. With some magnetic materials it is possible to demagnetize the magnets partially, thereby adjusting the generator voltage. However, with some materials, as samarium cobalt, for example, partial demagnetization is not possible.
It is also known to adjust the reluctance of a magnetic leakage path in the stator, reducing the generator operating flux and the generated voltage. This approach, however, does not permit an interchange of rotors from one stator to another. Readjustment is required if the rotor is replaced.